A plasma enhanced atomic layer deposition (PE-ALD) method is known as a kind of method of forming a film on a substrate. In the PE-ALD method, the substrate is exposed to a precursor gas which contains constitutional elements of a thin film desired to form on a substrate so as to allow the precursor gas to be chemically adsorbed on the substrate. Subsequently, the substrate is exposed to a purge gas so as to remove the precursor gas chemically adsorbed excessively on the substrate. Also, the substrate is exposed to plasma of a reactive gas containing the constitutional elements of the desired thin film so as to form a desired thin film on the substrate. In the PE-ALD method, these steps are repeated so as to generate a film formed by processing the atoms or molecules included in the precursor gas, on the substrate.
A single wafer type film forming apparatus and a semi-batch type film forming apparatus are known as apparatuses for performing the PE-ALD method. Among these film forming apparatuses, the semi-batch type film forming apparatus is excellent in throughput compared to the single wafer type film forming apparatus since the semi-batch type film forming apparatus is capable of forming a film on a plurality of substrates simultaneously. Specifically, in the semi-batch type film forming apparatus, a region in which a precursor gas is supplied and a region in which plasma of a reactive gas is generated are separately provided in a processing chamber and a plurality of substrates are moved to sequentially pass through these regions. As described above, since the semi-batch type film forming apparatus is capable of performing the supply of the precursor gas and the generation of the plasma of the reactive gas in different regions simultaneously, the semi-batch type film forming apparatus has an advantage in that its throughput is high compared to that of the single wafer type film forming apparatus.
Patent Document 1 and Patent Document 2 below disclose semi-batch type film forming apparatuses. The film forming apparatus described in Patent Document 1 is provided with a susceptor unit and a gas injection unit. The susceptor unit is used for supporting a substrate and is configured to rotate around a rotation axis. The gas injection unit is disposed to face the susceptor unit and includes a first region in which a precursor gas is supplied, a purge region in which a purge gas is supplied, a second region in which a reactive gas is supplied, and another purge region in which the purge gas is supplied. The first region, the purge region, the second region, and the another purge region are arranged in a circumferential direction and exhaust lines extending in a radial direction are provided between respective regions.
The film forming apparatus described in Patent Document 2 is provided with a rotating tray, a shower head, and a plasma source. The rotating tray is used for supporting the substrate and is rotatable around the rotation axis. The shower head and the plasma source are disposed to face the rotating tray and arranged in a circumferential direction. The shower head has a planar shape which is substantially a fan shape and supplies the precursor gas. The plasma source also has substantially a fan shape in a plan view, and supplies a high frequency power from a comb-shaped electrode while the reactive gas is supplied to generate plasma of the reactive gas. Exhaust holes are formed around the circumferences of the shower head and the plasma source, and a shower plate is provided between the shower head and the plasma source to supply the purge gas.